Particulate filters are utilized to remove particulate matter from an engine's exhaust flow. After an extended period of use, however, the particulate filter can become saturated with particulate matter, thereby reducing the flow of exhaust through the filter and subsequent engine performance. The collected particulate matter can be removed from the particulate filter through a process called regeneration.
Regeneration is the burning away of trapped particulate matter at high temperatures, typically in excess of 600° C. These temperatures can be periodically achieved through engine control, electric grids, fuel-fired burners, or other regeneration devices located at or upstream of the filter to heat the exhaust flowing through the filter. A rate of regeneration and a regeneration temperature resulting from combustion of the particulate matter can be dependent on multiple variables, including an amount of particulate matter accumulated within the filter at the time of regeneration, a temperature of the exhaust passing through the filter, and an amount of oxygen available for combustion during regeneration. For example, for a greater amount of collected particulate matter, a higher exhaust temperature, and a higher concentration of oxygen available during regeneration, regeneration will occur at a faster rate and attain higher combustion temperatures than if less particulate matter, a lower exhaust temperature, or less oxygen is present. In some situations, care should be taken such that a rate of filter heating and a maximum combustion temperature achieved during regeneration does not cause damage to the filter.
One attempt at controlling regeneration rates and temperatures is disclosed by U.S. Patent Publication No. 2008/0010971 (the '971 publication) by Gioannini et al., published on Jan. 17, 2008. The '971 publication discloses a method for managing regeneration of a diesel particulate filter for a gas exhaust system of an internal combustion engine. The method includes monitoring a soot loading of the particulate filter and, when the soot loading exceeds a threshold level, initiating regeneration at a first rate. When regenerating at the first rate, a target temperature within the particulate filter and an oxygen flow to the filter are controlled to slow the rate of regeneration. The target temperature during the first rate is 600° C., and an allowed oxygen flow rate is any value lower than 7%. The regeneration duration at the first rate is based on a driving profile of the associated machine, with a maximum limit of 400 seconds. The regeneration temperatures are controlled by way of selective post fuel injections within the internal combustion engine.
After the amount of particulate matter remaining within the filter has been sufficiently reduced during regeneration at the first rate or the maximum duration limit has been exceeded, the method includes initiating regeneration at a second rate that is faster than the first rate. When regenerating at the second rate, the target temperature within the particulate filter is 650° C., and the allowed oxygen flow rate is a maximum concentration that can physically be obtained. The regeneration duration at the second rate is also based on a driving profile of the associated machine, with a maximum limit of 200 seconds.
By limiting the rate of regeneration when there is a large amount of particulate matter trapped within the filter, the maximum temperatures resulting from combustion of the trapped particulate matter can be maintained at a level that does not damage the filter. And, when the amount of particulate matter contained within the filter has sufficiently been reduced, the rate of regeneration and the resulting temperatures can be safely increased to speed up the regeneration process without causing damage to the filter.
The method of the '971 publication may lack efficiency. Specifically, the particulate matter contained within the filter reduces in a substantially exponential manner during regeneration. As such, toward the end of regenerating at the first rate, enough of the particulate matter may have been reduced that a higher rate of regeneration could have been safely implemented before regeneration at the second rate has begun. Thus, a regeneration method that varies temperature and/or oxygen control in a step-wise manner may result in unnecessarily long regeneration durations at slow rates. And, longer regeneration durations may require more power to sustain, thereby increasing operational costs of the associated internal combustion engine.
The disclosed exhaust system is directed toward overcoming one or more of the problems set forth above and/or other problems in the art.